The present invention relates to a linear light source unit for emitting a linear light beam, which unit is used in a facsimile transmitter, copy machine, image scanner, barcode reader, and others, as a light source for reading images.
In recent years, the light emitting diode (LED) is widely used as a light source for reading the image in a personal facsimile. This tendency is caused by the facts that the LED is suitable for miniaturizing the device, necessary light quantity reduces because the sensitivity of the CCD type sensor is increased, and hence the number of used LED reduces, which causes the manufacturing cost of the device to decrease.
In the linear light source unit, a light leading member is provided for leading the light beam to a linear light beam.
FIG. 8 is a perspective view showing a conventional linear light source unit. In FIG. 8, reference numeral 20 designates a linear light source unit which comprises a transparent light leading member 21 made of plastic and formed into a flat plate, and a plurality of LEDs 23 linearly mounted on a print substrate 22. In order to uniformly distribute light quantity on the LED arranged line, an incidence portion 21b of the light leading member is formed into a semicircular shape, inclined walls 21c are formed on both sides to form guide surfaces, and a light discharge surface 21a is formed into a saw teeth surface or embossing surface. Namely, the distribution of quantity of light is adjusted by using diffusion, refraction and reflection of light.
However, the above described conventional linear light source unit can not achieve a uniform light distribution, and has a problem that an immediately upper portion of the light source becomes most bright.
In addition, in order to improve the uniformity of the light quantity, a plurality of LEDs must be provided, which results in increase of the manufacturing cost of the linear light source unit.